Cardiac arrhythmias are caused by localized electrophysiologic phenomena. These are of generally two types: additional foci or reentrant circuits. Reentrant circuits can be highly localized, as in ventricular tachycardia postinfarction or AV node reentry, or can be of a grosser morphology, as in accessory pathway pathologies. Since they are localized phenomena, they can be treated surgically. The task is to remove or destroy the offending region, thereby eliminating the source of the arrhythmia.
Current surgical therapies include: cardiotomy; open chest cryoablation; closed-chest catheter radio frequency (rf) ablation; and closed-chest direct current ablation. Radio frequency catheter ablation is becoming the therapy of choice. The greatest drawback of rf ablation is that, prior to ablation, the site of the intended cardiac lesion must be determined by conventional electrocardiographic mapping. Unfortunately, conventional mapping does not provide definitive isolation of the problem area. In a great majority of cases, more than one lesion must be made in order to effect a cure. Multiple lesions are required because the effectiveness of each of the proposed lesion sites cannot be predetermined due to the limitations of conventional electrocardiographic mapping. Often five lesions, and sometimes as many as twenty lesions may be required before a successful result is obtained. Usually only one of the lesions is actually effective; the other lesions result in unnecessarily destroyed cardiac tissue.
Treatment of cardiac arrhythmias through selective ablation of cardiac tissue may be improved if, prior to ablation, the local electrical activity of the region can be suppressed to determine the effectiveness of the proposed lesion site in stopping the arrhythmia. Localized electrical activity may be suppressed by chilling small regions of myocardial tissue and then performing electrocardiographic mapping to evaluate the arrhythmia. This technique of cooling and mapping is called "zero-degree" or "ice" mapping. If the proposed lesion site would be effective, as determined by the ice mapping, to eliminate the arrhythmia, the site is ablated. Despite the advantages of cryoablation, it has not been the technique of choice for want of a single, easily operated device which effectively combines the functions of cryogenic cooling of cardiac tissue and tissue ablation.